Circuit breakers, line switches, disconnect switches and capacitor switches are well known components of electric transmission and distribution systems. Within these devices, spring-driven acceleration mechanisms have been used to accelerate penetrating contactors to sufficient velocity to extinguish an arcing contact occurring across a contactor gap within the switch without experiencing an undesirable restrike, which could otherwise cause disturbances on the electric power system. This typically requires extinguishing the arc after one-half cycle, which prevents a restrike from occurring after the initial arc break that occurs at the first half-cycle zero voltage crossing after initial separation of the contacts. For this type of device, it is helpful to house the penetrating contactor within a sealed container filled with a dielectric gas such as sulphur hexafluoride (SF6), which is directed into the contactor gap by a nozzle to help extinguish the arc. Extinguishing the arc in this manner, which is specifically designed to effectively absorb the arc energy, reduces the contactor gap separation required to extinguish the arc from what would be required to extinguish the arc in another environment such as air.
The basic design challenge for this type of device involves engineering an acceleration mechanism that obtains the desired contractor velocity quickly enough to extinguish the arc without experiencing an undesired restrike within acceptable weight, size and cost constraints. An example of this type of device employing a bidirectional spring-driven toggle mechanism is shown in Rostron et al., U.S. Pat. No. 6,583,978 entitled “Limited Restrike Electric Power Circuit Interrupter Suitable For Use as a Line Capacitor and Load Switch,” which is incorporated herein by reference. Other types of spring-driven acceleration mechanism have been used to accelerate penetrating contactors for many years. For example, see U.S. Pat. Nos. 6,483,679; 6,316,742; and 6,236,010, which are also incorporated herein by reference. In general, spring-driven acceleration and toggle mechanisms for accelerating penetrating contactors for single- and three-phase electric power switch configurations are well known.
Although the power interrupter employing a bidirectional spring-driven toggle mechanism shown in Rostron et al. is an effective and commercially successful device, it has the drawback of requiring a relatively large enclosure to house relatively robust internal components of the device. The weight of this type of power interrupter requires that the insulator supporting the stationary contact of the underlying disconnect switch, on top of which the power interrupter is mounted, be upgraded to carry the additional weight of the power interrupter. In addition, the additional force required to move the actuator arm of the power interrupter, and thereby charge the main spring of the device, with the moving arm of the disconnect switch also typically requires an upgrade to the disconnect switch operating mechanism. As a result, this type of power interrupter is only suitable for new installations and those justifying an upgrade to the disconnect switch insulator and operating mechanism.
Moreover, in many electric power applications, such as standard line and load switch applications, internal switching is very important when opening the switch but of less importance when closing or resetting the switch. Therefore, a bidirectional toggle mechanism may not be necessary, whereas a single break device that internally breaks the power circuit only on the opening stroke may be better suited for these applications. In particular, a bidirectional toggle switch requiring an upgrade to the underlying disconnect switch might be too expensive in many instances in which a single break device installed as a retrofit without having to alter the existing disconnect switch might be a cost effective option. As a result, the ability to install the power interrupter as a retrofit without having to alter the existing disconnect switch would make the device a cost effective option for a large number of disconnect switches operating at distribution, sub-transmission and transmission voltages.
Accordingly, there is an ongoing need for cost effective electric power interrupters suitable for use as line and load switches at distribution, sub-transmission and transmission voltages. There is a further need for a power interrupter that can be installed as a retrofit without having to alter the existing disconnect switch.